New submission from Marek Scholle <mscho...@purestorage.com>:
Hi, I ran into discussion about scoping in Python (visibility of outer variables in nested functions, global, nonlocal) which made me to create for other some showcases. I realized there is a space for ambiguity which I extracted to this REPL: ---- >>> x = [] >>> def f(): x += [1] ... >>> f() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in f UnboundLocalError: local variable 'x' referenced before assignment >>> x = [] >>> def f(): x.append(1) ... >>> f() >>> x [1] ---- The documentation says about `x += [1]` it is "translated" to `x.__iadd__([1])`. It would be interesting to know if Python actually documents that `x += [1]` will err with `UnboundLocalError`. I think there is a natural argument that `x += <rhs>` should behave as an in-place version of `x = x + <rhs>` (where `UnboundLocalError` makes perfect sense), but diving into documentation it seems that `x += <rhs>` should be a syntax sugar for `x.__iadd__(rhs)` in which case `UnboundLocalError` should not happen and looks like some parser artifact. ---------- components: Interpreter Core messages: 412365 nosy: mscholle priority: normal severity: normal status: open title: Unclear behavior of += operator type: behavior versions: Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue46612> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
